Versatility of a carbon paste electrode coupled to differential pulse voltammetry for determination of lisinopril with its associations (hydrochlorothiazide and amlodipine)

Abstract

Lisinopril (LNP) is an angiotensin converting enzyme inhibitor formulated with a diuretic, hydrochlorothiazide (HCTZ), or with a calcium channel blocker, amlodipine (AML), in a single tablet for treatment of hypertension. In this work, for the first time, two analytical methods are proposed for the determination of pairs of antihypertensives (HCTZ and LNP or AML and LNP). Both methods are based on the use of a carbon paste electrode (CPE) coupled with differential pulse voltammetry (DPV). In cyclic voltammetry measurements, three very well-resolved and reproducible oxidative processes of AML, HCTZ and LNP were found at 0.65 V, 0.76 V and 0.99 V (vs. Ag/AgCl (3.0 mol L⁻¹ KCl)), respectively, which were related to irreversible redox processes and the current is mostly controlled by diffusion of the three drugs to the CPE surface. The pH, supporting electrolyte and instrumental parameters of DPV were optimized. Analytical parameters such as linearity ranges, correlation coefficients and detection limits were evaluated. The viability of the proposed methods was successfully assessed by simultaneous quantification of the studied drugs in commercially available pharmaceutical formulations and also in spiked tap water samples. These methods represent an effective, inexpensive, easily accessible and alternative tool with no extraction or preconcentration procedures for the determination of LNP with its associations (HCTZ or AML) for analytical routine analysis or as a protocol for the analysis of environmental samples.